Aerojet Rocketdyne Holdings Inc. named a new chief executive Monday, promoting an officer who joined the Rancho Cordova rocket-engine manufacturer in March.

Eileen Drake, who has been Aerojet’s chief operating officer, replaced President and CEO Scott Seymour effective immediately. Aerojet said Seymour had been dealing with health problems.

Her promotion comes as Aerojet grapples with a recent decline in revenue, a cost-cutting drive and a dispute with a customer over responsibility for the explosion of an unmanned rocket last fall.

It also makes the 48-year-old Drake, a former commander of a U.S. Army airfield in Virginia, one of a handful of women with the top job at a defense contractor. Lockheed Martin and General Dynamics, two much larger contractors, named female CEOs in early 2013.

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Aerojet spokesman Glenn Mahone said Seymour, 64, “has had some health issues” and told the board of directors he was retiring. Drake will take his place on the company’s board of directors as well.

“She has been here several months,” Mahone said. “She’s best positioned and has the most knowledge to lead the company.” He said Drake was calling customers and getting ready to speak to employees, and wasn’t yet available to speak to the media.

Seymour, a former Northrop Grumman executive who joined Aerojet in 2010, engineered the company’s $550 million takeover of Rocketdyne in 2013. The purchase vastly expanded Aerojet’s size and scope, but the past few months have been rocky.

In February, a former top executive named Warren Boley resigned, reportedly over differences with Seymour about the company’s direction. In March, the company said it would lay off 10 percent of its workforce over the next four years. About half of the 500 layoffs are expected to take place in Rancho Cordova, eliminating about 16 percent of the current workforce of 1,600.

And in April, the company, then known as GenCorp Inc., reported a first-quarter loss amid a decline in revenue.

Aerojet also is still dealing with the fallout from the explosion last fall of an unmanned rocket bound for the International Space Station. An executive with rocket owner Orbital ATK Inc. suggested in April that the explosion was caused by defects in the engine, which was made by the Soviet Union in the 1960s and refurbished by Aerojet. Aerojet officials have said they think debris from a foreign object got into the engine and caused the explosion.

Aerojet shares closed at $20.59, down 16 cents, on the New York Stock Exchange.